This article proposes a process to identify the standing stabilizer, namely, the controller in humans to keep upright posture stable against perturbations. We model the controller as a piecewise-linear feedback system, where the state of the center of mass (COM) is regulated by coordinating the whole body so as to locate the zero-moment point (ZMP) at the desired position. This was developed for humanoid robots and is possibly able to elaborate the fundamental control scheme used by humans to stabilize themselves. Difficulties lie on how to collect motion trajectories in a wide area of the state space for reliable identification and how to identify the piecewise-affine dynamical system. For the former problem, a motion measurement protocol is devised based on the theoretical phase portrait of the system. Regarding the latter problem, some clustering techniques including K-means method and EM (Expectation-and-Maximization) algorithm were examined. We found that a modified K-means method produced the most accurate result in this study. The method was applied to the identification of a lateral standing controller of a human subject. The result of the identification quantitatively supported a hypothesis that the COM-ZMP regulator reasonably models the human’s controller when deviations of the angular momentum about the COM are limited.
This paper reports the result and discussion about our second experiment of standing motion measurement and analysis. We aim at identifying the standing controller of a human. In order to tackle the dynamical complexity of the human body, the COM-ZMP (the center of mass and the zeromoment point) model, which is widely used for designing the whole-body controller of humanoid robots, and a piecewiselinear controller is applied. In the previous experiment, the authors proposed a method to collect a sufficient number of loci of COM in a phase space for the identification of a controller, and showed that the human's standing behavior qualitatively has a similar property with the COM-ZMP model. It was also found, however, that the collected loci had large variability due to the uncertainty of convergence point and were partially inconsistent with the model, so that it was still difficult to identify the controller. Then, the authors reassessed the model and measurement protocol, and conducted the second experiment in order to improve the reliability of the measurement by visually presenting the referential point to subjects and by redesigning the protocol. As the result, more reliable loci to be processed of identification were obtained. It was also found that the effect of variation of the COM height due to the limitation of leg length, which was thought to be another source of the inconsistency, certainly existed but was not critical to model the human behavior.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.